1. Field of the Invention:
This invention relates to a process and an apparatus for the horizontal continuous casting of a metal molding having a small thickness or diameter.
2. Description of the Prior Art:
There is known a continuous casting process which employs a cooling mold having a horizontally extending cavity. Molten metal is supplied into the mold at one end thereof and solidified therein, and the slab or ingot thereby produced is drawn out through the opposite end of the mold continuously in a horizontal direction. This process is widely used for the production of ferroalloy and nonferrous alloy moldings. The molten metal supplied into the mold forms a solid skin along the inner surface of the mold, and the unsolidified metal surrounded by the solid skin is completely solidified by secondary cooling outside the mold. The process has, therefore, the disadvantage of impurities becoming concentrated in the last portion of the slab or ingot to be solifided, and gives rise to defects, such as segregation and blowholes, therein. Another drawback of this process is due to the fact that the slab (or ingot) is drawn out of the mold intermittently after the solid skin has grown to a sufficient thickness to prevent the cracking of the slab surface and the breakout of the molten metal which are likely to occur as a result of the friction developed between the mold and slab surfaces when the slab is drawn out of the mold. This intermittent operation, however, results in the formation of oscillation marks which are likely to cause the cracking of the slab when it is subjected to plastic deformation working. It is, therefore, necessary to remove the surface defects of the slab by, for example, grinding, scalping or melting prior to its plastic deformation working. In the event the slab is of a material having a wide solidification temperature range, such as cast iron or phosphor bronze, it is impossible to avoid the breakout of the molten metal unless the slab is drawn out after the molten metal has been completely solidified in the mold.
The inventor of this invention previously proposed an improved continuous casting process for producing metal molded structure having a smooth surface free from any surface defect formed by the friction between the mold and the slab to be cast therein. According to this process, the inner wall of a hollow mold in the vicinity of its outlet opening is heated by an embedded heater and thereby maintained at a temperature above the solidification temperature of the metal to be cast, so that the molten metal supplied from a molten metal holding furnace does not form a solid skin on the inner wall of the mold, but form a slab surface beginning to solidify immediately outwardly of the outlet of the mold. This process enables the continuous casting of an elongated slab having a smooth surface and a unidirectionally solidified structure. This process is disclosed in Japanese Patent Publication No. 46265/80 published on Nov. 21, 1980.
The inventor has thought of applying this process to the horizontal continuous casting of a molded metal structures. It has, however, been found difficult to produce such a structure free of blowholes, since the gas released from the molten metal during its solidification is prevented by the top wall of the mold from escaping out into the ambient air. Moreover, as the solidification of the slab surface takes place in the vicinity of the outlet of the mold, even a slight change in mold temperature, cooling water temperature or casting rate is likely to cause the molten metal to break out through the outlet of the mold. In order to avoid such breakout, it is imperative to be precisely aware of the position and configuration of the boundary between the solidified metal and the unsolidified metal in the mold.